In a database management system, a non-unique index over a table tends to exhibit large lists of record identifiers (“RIDs”) for each distinct key value. These lists require significant storage, as each RID and additional information (such as various RID flags) can require several bytes. For example, in a database management system such as DB2v9 from International Business Machines, Inc. a RID requires 7 bytes. By applying data specific compression techniques to the RID lists (e.g., delta encoding), the size of the index can be reduced dramatically. However, before actually compressing an existing index, or creating a new index in compressed format, the database administrator needs to have an indication of what compression factor is likely to be obtained. Unfortunately, conventional database management tools generally do not provide the administrator with the ability to estimate the compression factor of the various compression techniques.
Therefore a need exists to overcome the problems with the prior art as discussed above.